Integrated Volumetric Energy Recovery and Compression Device

ABSTRACT

Power-generation systems including a power plant and a power conversion unit including an energy recovery device and volumetric compressor are disclosed. In one embodiment, the volumetric fluid compressor has first and second meshed rotors and is configured to generate a stream of relatively high-pressure fluid including oxygen to the power plant. In one embodiment, the volumetric fluid energy recovery device having third and fourth meshed rotors, operatively connected to the compressor, and configured to be rotated by the exhaust gas or other fluid deriving energy from the exhaust gas. The system can additionally include a set of timing gears configured to operatively connect the first and second rotors of the compressor to the third and fourth rotors of the energy recovery device, and prevent contact between the first and second rotors and between the third and fourth rotors. The system may also include a rotation transferring link for operative connection between the compressor and the energy recovery device.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is being filed on 14 Mar. 2014, as a PCT International Patent application and claims priority to U.S. Patent Application Ser. No. 61/787,834 filed on 15 Mar. 2013, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a power-generation system including a volumetric energy recovery device coupled to a power plant.

BACKGROUND

Fluid devices, such as expansion turbines, are frequently used to generate useful work in various power-generation processes. In such power-generation processes a high pressure working fluid is typically expanded in the fluid device to produce useful work. Because the work is extracted from the expanding high pressure fluid, the fluid expansion is approximated by an isentropic process, i.e., a constant entropy process.

Representative power-generation processes may include the Rankine cycle, where the working fluid may be water and the combustion of natural gas, fuel oil or coal is used to generate high-pressure steam to be subsequently channeled to the device. After the energy of the high temperature working fluid has been converted to useful work within the fluid device, the working fluid is typically exhausted from the device in low pressure form at a significantly reduced temperature, sometimes below −90° C.

SUMMARY

A power-generation system includes a power plant employing a power-generation cycle, wherein the power plant uses oxygen to generate power and generates an exhaust gas as a byproduct of the power-generation cycle. The system can also include a volumetric fluid compressor having first and second meshed rotors and configured to generate a stream of relatively high-pressure fluid including oxygen to the power plant. The system also may also include a volumetric fluid energy recovery device having third and fourth meshed rotors, operatively connected to the compressor, and configured to be rotated by the exhaust gas, i.e., to recoup energy from the exhaust gas, to drive the compressor. The system can additionally include a set of timing gears configured to operatively connect the first and second rotors of the compressor to the third and fourth rotors of the energy recovery device, and prevent contact between the first and second rotors and between the third and fourth rotors. The system may also include a rotation transferring link for operative connection between the compressor and the energy recovery device. The link can be configured to substantially match rotating speed of the energy recovery device with the rotating speed of the power plant that is determined by an amount of oxygen used by the power plant to generate the power.

Another embodiment of the disclosure is directed to a vehicle having a power plant that employs a power-generation cycle to propel the vehicle. The vehicle can include a volumetric fluid compressor and a volumetric energy recovery device of the kind described above.

The above features and advantages, and other features and advantages of the present disclosure, will be readily apparent from the following detailed description of the embodiment(s) and best mode(s) for carrying out the described invention when taken in connection with the accompanying drawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic depiction of a first embodiment of a vehicle power plant having a volumetric energy recovery device and a volumetric fluid compressor having features that are examples of aspects in accordance with the principles of the present disclosure.

FIG. 2 is a schematic depiction of a second embodiment of a vehicle power plant having a volumetric energy recovery device and a volumetric fluid compressor having features that are examples of aspects in accordance with the principles of the present disclosure.

FIG. 3 is a schematic depiction of a third embodiment of a vehicle power plant having a volumetric energy recovery device and a volumetric fluid compressor having features that are examples of aspects in accordance with the principles of the present disclosure.

FIG. 4 is a schematic depiction of a first embodiment of an integrated device including a volumetric energy recovery device and volumetric fluid compressor usable in the power plants of FIGS. 1-3.

FIG. 5 is a schematic depiction of a second embodiment of an integrated device including a volumetric energy recovery device and a volumetric fluid compressor usable in the power plants of FIGS. 1-3.

FIG. 5A is an end view of a planetary gear set usable in the integrated device shown in FIG. 5.

FIG. 6 is a schematic cross-sectional side view of an energy recovery device usable in the power plants of FIGS. 1-3, and 8-9.

FIG. 7 is schematic perspective view of an energy recovery device usable in the power plants of FIGS. 1-3, and 8-9.

FIG. 8 is a schematic depiction of a fourth embodiment of a vehicle power plant having a volumetric energy recovery device and a volumetric fluid compressor having features that are examples of aspects in accordance with the principles of the present disclosure.

FIG. 9 is a schematic depiction of a fifth embodiment of a vehicle power plant having a volumetric energy recovery device and a volumetric fluid compressor having features that are examples of aspects in accordance with the principles of the present disclosure.

FIG. 10 is a schematic of a rotor geometry usable with the energy recovery device shown in FIG. 6.

FIG. 11 is a schematic depiction of a third embodiment of an integrated device including a volumetric energy recovery device and a volumetric fluid compressor usable in the power plants of FIGS. 1-3.

DETAILED DESCRIPTION

Various embodiments will be described in detail with reference to the drawings, wherein like reference numerals represent like parts and assemblies throughout the several views. Reference to various embodiments does not limit the scope of the claims attached hereto. Additionally, any examples set forth in this specification are not intended to be limiting and merely set forth some of the many possible embodiments for the appended claims.

Modern demands for fuel efficient vehicles and power plants have led to development of hybrid power-generation and propulsion systems. Generally, such systems combine a power plant, such as an internal combustion engine or a fuel cell, and an electric motor to drive the vehicle. Each of the internal combustion engine and fuel cell emits high temperature exhaust as a byproduct of the power-generation cycle employed therein. The high temperature exhaust constitutes energy that is lost from the power-generation cycle, which, if recaptured, could be employed to improve efficiency of the cycle, and, therefore, of the propulsion system employing the same.

Referring to the drawings wherein like reference numbers correspond to like or similar components throughout the several figures. Improvements in other applications are also desired, for example in marine agricultural and industries. Another example is stationary generator sets.

FIGS. 1-3 and 8-9 show examples of power-generation systems 14 that include a power conversion unit 15. Each of the disclosed power conversion units 15 includes an energy recovery device 20 and a compression device 50. As presented, the energy recovery device 20 converts waste heat energy from the power plant 16 to rotational energy that can be utilized to drive the compression device 50 directly or indirectly. FIGS. 1-3 show examples of integrated power conversion units 15 in which the energy recovery device 20 is directly coupled to a compression device 50. By use of the term “compression device” it is meant to include any type of device capable of compressing a gas fluid stream, such as volumetric devices (e.g. Roots-style blowers) and non-volumetric devices (e.g. screw type compressors, turbines, scroll type compressors, etc.). By use of the term “integrated” it is meant to include systems where the output of the device 20 and the input for the compression device 50 are mechanically coupled together. FIGS. 8-9 show examples of distributed power conversion units 15 in which the energy recovery device 20 and the compression device 50 are each coupled to the power plant 16. By use of the term “distributed” it is meant to include systems that do not share a direct mechanical link between the device 20 and the compression device 50. The power-generation systems 14 may be associated with a vehicle, agricultural equipment, and/or stationary power generation systems, such as generator sets.

Referring to FIG. 1, a vehicle 10 is shown having wheels 12 for movement along an appropriate road surface. The vehicle 10 includes a power-generation system 14. The system 14 includes a power plant 16 employing a power-generation cycle. The power plant 16 uses a specified amount of oxygen, which may be part of a stream of intake air 11, to generate power. The power plant 16 also generates waste heat in the form of a high-temperature exhaust gas in exhaust line 18. In one embodiment, the power plant 16 is an internal combustion (IC) engine, such as a spark-ignition or compression-ignition type which combusts a mixture of fuel and air to generate power. In one embodiment, the power plant 16 may be a fuel cell which converts chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent.

In one embodiment, and as shown in FIG. 1, all of the exhaust from power plant 16 is directed to the power conversion unit 15 via exhaust line 18. As the exhaust passes through the energy recovery side of the unit 15, the exhaust gas causes internal rotors 30, 32 to rotate, which in turns causes internal rotors 60, 62 of the compression device 50 to rotate. The gas can then exit the system at exhaust line 17. As shown at FIG. 1, an exhaust bypass line 18 a and a bypass valve 202 are provided to allow exhaust gases to be diverted around the energy recovery device 20, when desired. The rotation of the rotors 60, 62 causes an intake air stream 11 to be compressed and delivered to the power plant 16 via intake manifold 13. As shown at FIG. 1, an intake air bypass line 13 a and bypass valve 204 may be provided to allow compressed air to recirculate back to the compression device inlet at line 11 in order to prevent over-compression of the intake air. It is noted that the description of the energy recovery device 20 and the compression device 50 will be discussed in detail in later sections, as will be the operation of the bypass valves 202 and 204.

In one embodiment, and as shown in FIG. 2, only a portion of the exhaust from the power plant 16 is directed to the power conversion unit 15 via exhaust line 18 a. As shown, line 18 a carries exhaust gas that is to be recirculated into the intake manifold 13 of the power plant 16 in an exhaust gas recirculation (EGR) configuration. Accordingly, after the exhaust passes through the energy recovery device 20, the exhaust gas can be delivered to an exhaust gas cooler 19 via line 18 b and then provided to an EGR mixer 21 via line 18 c where the exhaust gas can be missed with fresh intake air from compression device 50. It is noted that energy recovery device 20 extracts energy from the exhaust gas stream and can allow for the EGR cooler 19 to be made smaller than might otherwise be possible without an energy recovery device 20. The energy recovery device can also be used to regulate the amount of EGR mixed into the fresh intake air. It is noted that the system shown in FIG. 2 may also be provided with the bypass lines 13 a and/or 18 a and the bypass valves 202 and/or 204 shown in FIG. 1.

In one embodiment, and as shown in FIG. 3, an organic Rankine cycle (ORC) is used to power the energy recovery device 20 rather than exhaust gas directly. In such an embodiment, a piping system 100 including a heat exchanger 102 is provided that transfers heat from the exhaust gas line 18 to a working fluid that is then delivered to the energy recovery device 20. A condenser 104 is also provided which creates a low pressure zone for the working fluid and thereby provides a location for the working fluid to condense. Once condensed, the working fluid can be delivered to the heat exchanger 102 via a pump 106. A more detailed description of an ORC system being utilized to drive an energy recovery device 20 is provided in Patent Cooperation Treaty (PCT) International Application Number PCT/US13/28273 entitled VOLUMETRIC ENERGY RECOVERY DEVICE AND SYSTEMS. PCT/US13/28273 is incorporated herein by reference in its entirety. It is noted that the system shown in FIG. 3 may also be provided with the bypass line 18 a and the bypass valve 202 shown in FIG. 1.

Referring to FIG. 8, an embodiment is shown in which the compression device 50 and the energy recovery device 20 are separate units and are therefore not integrated with each other. Accordingly, compression device 50 may be a standard Roots-type blower 50. In one embodiment, the compression device 50 is of the type shown and described in U.S. Pat. No. 7,488,164 entitled OPTIMIZED HELIX ANGLE ROTORS FOR ROOTS-STYLE SUPERCHARGER, which is incorporated herein by reference in its entirety. In one embodiment, the energy recovery device 20 is of the type shown and described in the above referenced application PCT/US13/28273. As shown, a power output location 16 b of the power plant 16 drives the compression device 50, while the output of the energy recovery device 20 is sent to a power input location 16 a of the power plant. In one embodiment, the power input location 16 a is the drive shaft of the engine and the power output location 16 b is a pulley, belt, gear, or chain connected directly or indirectly to the power plant 16 crankshaft. Alternatively, or in addition to, the energy recovery device can send power to an energy storage device 110, such as a battery or accumulator. It is noted that the system shown in FIG. 8 may also be provided with the bypass lines 13 a and/or 18 a and the bypass valves 202 and/or 204 shown in FIG. 1.

FIG. 9 is similar to FIG. 8 in that a distributed system is shown, but shows the use of two energy recovery devices 20A and 20B. The exhaust flow configuration for the first energy recovery device 20A is the same as that shown for FIG. 2 while the exhaust flow stream for the second energy recovery device 20B is the exhaust flow not utilized in the EGR system. As shown, both the energy recovery devices 20A, 20B provide power back to the power plant 16 at a location 16 a, which may be a common location or separate locations. It is noted that the system shown in FIG. 9 may also be provided with the bypass lines 13 a and/or 18 a and the bypass valves 202 and/or 204 shown in FIG. 1.

Referring to FIGS. 4, 5, and 11, schematics of three embodiments of an integrated power conversion unit 15, 115 usable with the above described systems are shown. FIGS. 7 and 8 show further details regarding the volumetric energy recovery device 20. It is noted that many features of the volumetric energy recovery device 20 are shared with the compression device 50.

Power Conversion Unit—Energy Recovery Device

In general, the volumetric energy recovery device 20 relies upon the kinetic energy and static pressure of the working fluid 12-1 to rotate a shaft 38 or 40. Where the device 20 is used in an expansion application, such as with a Rankine cycle, additional energy is extracted from the working fluid via fluid expansion. In such instances, device 20 may be referred to as an expander or expansion device, as so presented in the following paragraphs. However, it is to be understood that the device 20 is not limited to applications where a working fluid is expanded across the device, for example the exhaust driven embodiments shown in FIGS. 1 and 2.

The device 20 has a housing 22 with a fluid inlet 24 and a fluid outlet 26 through which the working fluid 12-1 undergoes a pressure drop to transfer energy to the shaft 38 or 40. The shaft 38 is driven by synchronously connected first and second interleaved counter-rotating rotors 30, 32 which are disposed in a cavity 28 of the housing 22. Each of the rotors 30, 32 has lobes that are twisted or helically disposed along the length of the rotors 30, 32. Upon rotation of the rotors 30, 32, the lobes at least partially seal the working fluid 12-1 against an interior side of the housing, at which point expansion of the working fluid 12-1 only occurs to the extent allowed by leakage which represents an inefficiency in the system, in an ORC application. In contrast to some expansion devices that change the volume of the working fluid when the fluid is sealed, the volume defined between the lobes and the interior side of the housing 22 of device 20 is constant as the working fluid 12-1 traverses the length of the rotors 30, 32. Accordingly, the device 20 may be referred to as a “volumetric device” as the sealed or partially sealed working fluid volume does not change. It is noted that, and as will be clear to one skilled in the art upon learning of this disclosure, the described geometry and construction of the device 20 is dissimilar from the geometry and construction of a typical roots-type compressor.

The device 20 is shown in detail in FIGS. 6 and 7. The device 20 includes a housing 22. As shown in FIG. 6, the housing 22 includes an inlet port 24 configured to admit relatively high-pressure working fluid 12-1 from the heat exchanger 102 (shown in FIG. 3) or direct exhaust (FIGS. 1 and 2) from power plant 16. The housing 22 also includes an outlet port 26 configured to discharge working fluid 12-2. It is noted that the working fluid discharging from the outlet 26 is at a relatively higher pressure than the pressure of the working fluid at the condenser 104, where an ORC system is utilized. Additionally, the inlet and outlet ports 24, 26 may be provided with connectors for providing a fluid tight seal with other system components to ensure the working fluid 12-1, 12-2, which may be ethanol, does not dangerously leak outside of the device 20.

As additionally shown in FIG. 7, each rotor 30, 32 has four lobes, 30-1, 30-2, 30-3, and 30-4 in the case of the rotor 30, and 32-1, 32-2, 32-3, and 32-4 in the case of the rotor 32. Although four lobes are shown for each rotor 30 and 32, each of the two rotors may have any number of lobes that is equal to or greater than two, as long as the number of lobes is the same for both rotors. Accordingly, when one lobe of the rotor 30, such as the lobe 30-1 is leading with respect to the inlet port 24, a lobe of the rotor 30, such as the lobe 30-2, is trailing with respect to the inlet port 24, and, therefore with respect to a stream of the high-pressure working fluid 12-1.

As shown, the first and second rotors 30 and 32 are fixed to respective rotor shafts, the first rotor being fixed to a shaft 38 and the second rotor being fixed to a shaft 40. Each of the rotor shafts 38, 40 is mounted for rotation on a set of bearings (not shown) about an axis X1, X2, respectively. It is noted that axes X1 and X2 are generally parallel to each other. The first and second rotors 30 and 32 are interleaved and continuously meshed for unitary rotation with each other. With renewed reference to FIG. 6, the device 20 also includes meshed timing gears 42 and 44, wherein the timing gear 42 is fixed for rotation with the rotor 30, while the timing gear 44 is fixed for rotation with the rotor 32. The timing gears 42, 44 are configured to retain specified position of the rotors 30, 32 and prevent contact between the rotors during operation of the device 20.

The shaft 38 is rotated by the working fluid 12-1 as the working fluid transitions from the relatively high-pressure working fluid 12-1 to the relatively low-pressure working fluid 12-2. As may additionally be seen in both FIGS. 6 and 7, the shaft 38 extends beyond the boundary of the housing 22. Although the shaft 38 is shown as being operatively connected to the first rotor 30, in the alternative the shaft 38 may be operatively connected to the second rotor 32. As schematically shown in FIGS. 8-9, the shaft 38 can be coupled to the power plant 16 such that the energy from the exhaust can be recaptured. A gear reducer can be provided to provide a better match between rotational speeds of the power plant 16 and the shaft 38.

In one aspect of the geometry of the device 20, each of the rotor lobes 30-1 to 30-4 and 32-1 to 32-4 has a lobe geometry in which the twist of each of the first and second rotors 30 and 32 is constant along their substantially matching length 34. As shown schematically at FIG. 10, one parameter of the lobe geometry is the helix angle HA. By way of definition, it should be understood that references hereinafter to “helix angle” of the rotor lobes is meant to refer to the helix angle at the pitch diameter PD (or pitch circle) of the rotors 30 and 32. The term pitch diameter and its identification are well understood to those skilled in the gear and rotor art and will not be further discussed herein. As used herein, the helix angle HA can be calculated as follows: Helix Angle (HA)=(180/.pi.*arctan(PD/Lead)), wherein: PD=pitch diameter of the rotor lobes; and Lead=the lobe length required for the lobe to complete 360 degrees of twist. It is noted that the Lead is a function of the twist angle and the length L1, L2 of the lobes 30, 32, respectively. The twist angle is known to those skilled in the art to be the angular displacement of the lobe, in degrees, which occurs in “traveling” the length of the lobe from the rearward end of the rotor to the forward end of the rotor. As shown, the twist angle is about 120 degrees, although the twist angle may be fewer or more degrees, such as 160 degrees.

In another aspect of the expander geometry, the inlet port 24 includes an inlet angle 24-1, as can be seen schematically at FIG. 6, and in the embodiments shown at FIGS. 4-5. In one embodiment, the inlet angle 24-1 is defined as the general or average angle of an inner surface 24 a of the inlet port 24, for example an anterior inner surface as shown at FIG. 6. In one embodiment, the inlet angle 24-1 is defined as the angle of the general centerline of the inlet port 24, for example as shown at FIG. 2. In one embodiment, the inlet angle 24-1 is defined as the general resulting direction of the working fluid 12-1 entering the rotors 30, 32 due to contact with the anterior inner surface 24 a, as can be seen at both FIGS. 2 and 8. As shown, the inlet angle 24-1 is neither perpendicular nor parallel to the rotational axes X1, X2 of the rotors 30, 32. Accordingly, the anterior inner surface 24 a of the inlet port 24 causes a substantial portion of the working fluid 12-1 to be shaped in a direction that is at an oblique angle with respect to the rotational axes X1, X2 of the rotors 30, 32, and thus generally parallel to the inlet angle 24-1.

Furthermore, the inlet port 24 may be shaped such that the working fluid 12-1 is directed to the first axial ends 30 a, 30 b of the rotors 30, 32 and directed to the rotor lobe leading and trailing surfaces (discussed below) from a lateral direction. However, it is to be understood that the inlet angle 24-1 may be generally parallel or generally perpendicular to axes X1, X2, although an efficiency loss may be anticipated for certain rotor configurations. Furthermore, it is noted that the inlet port 24 may be shaped to narrow towards the inlet opening 24 b, as shown in both FIGS. 2 and 8. Referring to FIG. 10, it can be seen that the inlet port 24 has a width W that is slightly less than the combined diameter distance of the rotors 30, 32. The combined rotor diameter is equal to the distance between the axes X1 and X2 plus twice the distance from the centerline axis X1 or X2 to the tip of the respective lobe. In some embodiments, width W is the same as or more than the combined rotor diameter.

In another aspect of the expander geometry, the outlet port 26 includes an outlet angle 26-1, as can be seen schematically at FIG. 6, and in the embodiment shown at FIGS. 4-5. In one embodiment, the outlet angle 26-1 is defined as the general or average angle of an inner surface 26 a of the outlet port 26, for example as shown at FIG. 8. In one embodiment, the outlet angle 26-1 is defined as the angle of the general centerline of the outlet port 26, for example as shown at FIG. 6. In one embodiment, the outlet angle 26-1 is defined as the general resulting direction of the working fluid 12-2 leaving the rotors 30, 32 due to contact with the inner surface 26 a. As shown, the outlet angle 26-1 is neither perpendicular nor parallel to the rotational axes X1, X2 of the rotors 30, 32. Accordingly, the inner surface 26 a of the outlet port 26 receives the leaving working fluid 12-2 from the rotors 30, 32 at an oblique angle which can reduce backpressure at the outlet port 26. In one embodiment, the inlet angle 24-1 and the outlet angle 26-1 are generally equal or parallel, as shown in FIG. 6. In one embodiment, the inlet angle 24-1 and the outlet angle 26-1 are oblique with respect to each other. It is to be understood that the inlet angle 24-1 may be generally perpendicular to axes X1, X2, although an efficiency loss may be anticipated for certain rotor configurations. It is further noted that the outlet angle 26-1 may be perpendicular to the axes X1, X2. As configured, the orientation and size of the outlet port 26 are established such that the leaving working fluid 12-2 can evacuate each rotor cavity 28 as easily and rapidly as possible so that backpressure is reduced as much as possible. The output power of the shaft 38 is maximized to the extent that backpressure caused by the outlet can be minimized such that the working fluid can be rapidly discharged into the lower pressure working fluid at the condenser.

The efficiency of the device 20 can be optimized by coordinating the geometry of the inlet angle 24-1 and the geometry of the rotors 30, 32. For example, the helix angle HA of the rotors 30, 32 and the inlet angle 24-1 can be configured together in a complementary fashion. Because the inlet port 24 introduces the working fluid 12-1 to both the leading and trailing faces of each rotor 30, 32, the working fluid 12-1 performs both positive and negative work on the device 20.

To illustrate, FIG. 7 shows that lobes 30-1, 30-4, 32-1, and 32-2 are each exposed to the working fluid 12-1 through the inlet port opening 24 b. Each of the lobes has a leading surface and a trailing surface, both of which are exposed to the working fluid at various points of rotation of the associated rotor. The leading surface is the side of the lobe that is forward most as the rotor is rotating in a direction R1, R2 while the trailing surface is the side of the lobe opposite the leading surface. For example, rotor 30 rotates in direction R1 thereby resulting in side 30-1 a as being the leading surface of lobe 30-1 and side 30-1 b being the trailing surface. As rotor 32 rotates in a direction R2 which is opposite direction R1, the leading and trailing surfaces are mirrored such that side 32-2 a is the leading surface of lobe 32-2 while side 32-2 b is the trailing surface.

In generalized terms, the working fluid 12-1 impinges on the trailing surfaces of the lobes as they pass through the inlet port opening 24 b and positive work is performed on each rotor 30, 32. By use of the term positive work, it is meant that the working fluid 12-1 causes the rotors to rotate in the desired direction: direction R1 for rotor 30 and direction R2 for rotor 32. As shown, working fluid 12-1 will operate to impart positive work on the trailing surface 32-2 b of rotor 32-2, for example on surface portion 47. The working fluid 12-1 is also imparting positive work on the trailing surface 30-4 b of rotor 30-1, for example of surface portion 46. However, the working fluid 12-1 also impinges on the leading surfaces of the lobes, for example surfaces 30-1 and 32-1, as they pass through the inlet port opening 24 b thereby causing negative work to be performed on each rotor 30, 32. By use of the term negative work, it is meant that the working fluid 12-1 causes the rotors to rotate opposite to the desired direction, R1, R2.

Accordingly, it is desirable to shape and orient the rotors 30, 32 and to shape and orient the inlet port 24 such that as much of the working fluid 12-1 as possible impinges on the trailing surfaces of the lobes with as little of the working fluid 12-1 impinging on the leading lobe surfaces, such that the highest net positive work can be performed by the device 20.

One advantageous configuration for optimizing the efficiency and net positive work of the device 20 is a rotor lobe helix angle HA of about 35 degrees and an inlet angle 24-1 of about 30 degrees. Such a configuration operates to maximize the impingement area of the trailing surfaces on the lobes while minimizing the impingement area of the leading surfaces of the lobes. In one embodiment, the helix angle is between about 25 degrees and about 40 degrees. In one embodiment, the inlet angle 24-1 is set to be within (plus or minus) 15 degrees of the helix angle HA. In one embodiment, the helix angle is between about 25 degrees and about 40 degrees. In one embodiment, the inlet angle 24-1 is set to be within (plus or minus) 15 degrees of the helix angle HA. In one embodiment, the inlet angle is within (plus or minus) 10 degrees of the helix angle. In one embodiment, the inlet angle 24-1 is set to be within (plus or minus) 5 degrees of the helix angle HA. In one embodiment, the inlet angle 24-1 is set to be within (plus or minus) 15% of the helix angle HA while in one embodiment, the inlet angle 24-1 is within 10% of the helix angle. Other inlet angle and helix angle values are possible without departing from the concepts presented herein. However, it has been found that where the values for the inlet angle and the helix angle are not sufficiently close, a significant drop in efficiency (e.g. 10-15% drop) can occur.

Power Conversion Unit—Compression Device

As related previously, compression device 50 can have a similar construction to that described in U.S. Pat. No. 7,488,164, and has many overlapping features with the above described energy recovery device 20. Accordingly, the description of the energy recovery device 20 is hereby incorporated herein by reference in its entirety for the compression device 50.

Referring to FIGS. 4, 5, and 11, schematics of three embodiments of an integrated power conversion unit 15, 115 usable with the above described systems are shown. In one aspect, the power conversion unit 15 includes a compression device 50 having a housing 52. As shown, the housing 52 includes an inlet port 54 configured to admit relatively low-pressure ambient air 54-1. The housing 52 also includes an outlet port 56 configured to discharge relatively high-pressure air 56-1 to the power plant 16. It is noted that the locations of the inlet port 54 and the outlet port 56 may be provided either radially or axially, for example, an axial inlet and a radial outlet.

The housing 52 of the compression device 50 also includes a rotor cavity 58. As shown, disposed inside the rotor cavity 58 are first and second twisted meshed rotors 60 and 62, respectively. The rotors 60 and 62 are mounted for synchronous rotation in the rotor cavity 58 and configured to compress relatively low-pressure ambient air 54-1 into relatively high-pressure air 56-1. Accordingly, the first and second meshed rotors 60 and 62 are configured to generate a stream of relatively high-pressure air 56-1 that includes oxygen for subsequent delivery to the power plant 16, which then generates power by using the supply of compressed oxygen.

As shown, each rotor 60, 62 has a plurality of lobes 60-1, 62-1, respectively. In one embodiment, each rotor 60, 62 has three lobes 60-1, 62-1 while in another embodiment, each rotor 60, 62 has four lobes 60-1, 62-1. Accordingly, when one lobe of the rotor 60, such as the lobe 60-1 is leading with respect to the inlet port 54, a lobe of the rotor 60, such as the lobe 60-2, is trailing with respect to the inlet port 64, and, therefore with respect to a stream of the relatively low-pressure ambient air 54-1.

In one embodiment, the twist of each of the first and second rotors 60 and 62 is constant along their substantially matching length. The first and second rotors 60 and 62 are fixed to respective rotor shafts, the first rotor being fixed to an input shaft 68 and the second rotor being fixed to a shaft 69. Each of the rotor shafts 68, 69 is mounted for rotation on a set of bearings (not shown). The shaft 68 can be rotated by the power plant 16 in order generate the stream of relatively high-pressure air 56-1. Although the input shaft 68 is shown as being operatively connected to the first rotor 60, in the alternative the shaft 69 may be operatively connected to the second rotor 62. The first and second rotors 60 and 62 are interleaved and continuously meshed for unitary rotation with each other.

With reference to FIGS. 4 and 11, the compressor 50 also includes meshed timing gears 72 and 74, wherein the timing gear 72 is fixed for rotation with the rotor 60, while the timing gear 74 is fixed for rotation with the rotor 62. The timing gears 72, 74 are configured to maintain specified relative position between the rotors 60, 62 and prevent contact between the rotors during operation of the compressor 50.

It is noted that the energy recovery device 20 and the compression device 50 could have rotors and housing of similar construction, although some efficiency would likely be lost without utilizing optimized rotors and inlets.

Power Conversion Unit—Power Transmission Link

The power conversion unit 15 can include a power transmission link 80 between the energy recovery device 20 and the compression device 50 such that waste heat from the power plant 16 can be converted into rotational energy by the energy recovery device 20 that is then used to drive the compression device 50. Accordingly, the link 80 can be configured to substantially match the rotational speed of the device 50 with the rotational speed of the power plant 16, wherein the speed of the power plant is determined by the amount of oxygen used by the power plant to generate the requisite power. It is noted that FIGS. 4 and 5 show an integrated power conversion unit 15 in which the energy recovery device 20, the compression device 50, and the link 80 are in a common housing.

With reference to FIGS. 4 and 11, the link 80 is provided at the end opposite timing gears 72, 74 of the compression device 50 and at the end opposite timing gears 42, 44 of the recovery device 20. As shown, shaft 38 of the recovery device 20 is configured as an output shaft and shaft 69 of compression device 50 is configured as an input shaft. Torque can be transferred between shafts 38 and 69 by mechanically coupling the shafts together, for example through the use of a gear set having gears 81, 83 connected to shafts 38, 69, respectively. The gear set may be configured as a simple gear-train configured to define a particular speed ratio between the compression device 50 and the recovery device 20. Also, such a direct mechanical drive or simple gear-train may be used as the link 80 in the situation when the power plant 16 is a fuel cell. Other means for mechanically coupling the shafts are also possible, for example, shaft 38 or 40 could be aligned and coupled or welded directly to shafts 68 or 69, respectively. Also, shafts 38 and 68 can be provided as a single common shaft while shafts 40 and 69 can also be provided as a single common shaft.

It is noted that link 80 can be configured to replace the timing gears 42, 44, 72, 74 by extending the shaft 40 to gear 83 and extending the shaft 68 to gear 81. In such a configuration, both power transmission and rotor timing would be accomplished through the same gear set, such that a single pair of timing gears constitutes the set of timing gears of the system 14, and be sufficient to suitably synchronize the rotation of the first and second rotors 30, 32 of the device 20 to the third and fourth rotors 60, 62 of the device 50.

With reference to FIG. 5, the recovery device 20 and the compression device 50 are oriented such that the timing gears 72, 74 are adjacent to timing gears 42, 44. In this embodiment, the recovery device 20 and compression device 50 are mechanically coupled to each other through a variable speed drive 85, which is shown as a compound planetary gear set structure having a common or shared carrier member. Such a compound planetary gear set 85 may provide a variable gear ratio configured to substantially match the speeds of the power plant 16 and the device 20 depending on the operating conditions experienced by the power plant 16.

With reference to FIGS. 5 and 5 a, the shaft 68 can be coupled to sun gear 85 a of the planetary gear set 85, while shaft 38 can be coupled to a carrier 87 that is connected to a set of planet gears 85 b that are rotationally engaged with the sun gear 85 a. A ring gear 85 c is also provided that is shown as being rotationally engaged with the planet gears 85 b. When the position of the ring gear 85 c is fixed, all power from the shaft 38 is transmitted to the shaft 68 at a first gear ratio defined by the sun gear 85 a and the planetary gears 85 b. Where the ring gear 85 c is allowed to rotate, power can then be transmitted from shaft 38 to both shaft 68 and to the ring gear 85 c. Such a configuration allows for the desired rotational speed of the compression system 50 to be obtained while sending any excess power generated by the recovery device 20 to the ring gear 85 c.

In one embodiment, a generator or pump 82 may be placed in operative connection with the ring gear 85 c via a gear 89 that interfaces with teeth 85 d on the ring gear 85 c. Other types of drive systems are also possible, such as a belt and pulley. The generator 82 can then be configured to vary and select on demand the speed of the device 20 in order to substantially match the rotating speeds of the power plant 16 and the device 50. Also, the generator 82 may be operated as a brake to vary the speed of the device 20, such that the device 20 may be permitted to freewheel when the generator provides zero braking force. Furthermore, when the device 20 is permitted to freewheel because zero braking is being provided by the generator 82, parasitic drag from the device on the compression system 50 may be reduced, i.e., minimized, to increase operating efficiency of the entire system 14. When the ring gear is allowed to freewheel then zero torque is transferred similar to an open clutch condition. This would reduce losses during idle condition when available exhaust energy is too low to provide positive energy input back to the power plan 16.

With reference to FIGS. 4-6 and 11, the systems may also include a drive system 90 to allow the power plant 16 to drive the compression system 50 in the event that sufficient power is not available from the energy recovery device 20. In one embodiment, the drive system 90 includes an electric drive unit 91 that can drive the compression device 50 independently of engine operation. In another embodiment, and as shown at FIG. 11, the drive system 90 can include a drive unit 91 in the form of a pulley that is in power communication with the power plant 16 via a power output location (e.g. pulley 16 b and belt 16 c), as is found on typical roots-type blowers. Gear reducing systems are also possible. The embodiment of FIG. 11 is also shown as being provided with a clutch 93 such that the drive system 90 can be decoupled from the compression device 50 when desirable, such as when it is desired to fully drive the compression device 50 with only the expansion device 20. As an alternative to clutch 93, a one-way bearing set at the pulley may also be provided. Where so desired, link 80 can also include a clutch such that the recovery device 20 is not undesirably rotated by the drive system 90.

System Control and Operation

Any of the systems shown in FIGS. 1-3 and any of the configurations shown in FIGS. 4, 5, and 11 may be operated through a control system. Such a system is presented at FIG. 1 which shows an electronic controller. The electronic controller 500 is schematically shown as including a processor 500A and a non-transient storage medium or memory 500B, such as RAM, a flash drive or a hard drive. Memory 500B is for storing executable code, the operating parameters, and the input from the operator user interface 500D, while processor 500A is for executing the code. The electronic controller is also shown as including a transmitting/receiving port 500C, such as a vehicle CAN bus. A user interface 500D may also be provided to activate and deactivate the system, allow a user to manipulate certain settings or inputs to the controller 500, and to view information about the system operation.

The electronic controller 500 typically includes at least some form of memory 500B. Examples of memory 500B include computer readable media. Computer readable media includes any available media that can be accessed by the processor 500A. By way of example, computer readable media includes computer readable storage media and computer readable communication media.

Computer readable storage media includes volatile and nonvolatile, removable and non-removable media implemented in any device configured to store information such as computer readable instructions, data structures, program modules, or other data. Computer readable storage media includes, but is not limited to, random access memory, read only memory, electrically erasable programmable read only memory, flash memory or other memory technology, compact disc read only memory, digital versatile disks or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and that can be accessed by the processor 500A.

Computer readable communication media typically embodies computer readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media. The term “modulated data signal” refers to a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, computer readable communication media includes wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, radio frequency, infrared, and other wireless media. Combinations of any of the above are also included within the scope of computer readable media.

Electronic controller 500 is also shown as having a number of inputs/outputs that may be used for implementing desired operational modes of the power conversion unit 15. For example, electronic controller 500 provides outputs for commanding an expander bypass valve 202, a compressor bypass valve 204, and for controlling the drive system 90 (e.g. activating and deactivating clutch 93 and/or drive motor 91). Likewise, electronic controller 500 receives inputs for the control of the power conversion unit 15, for example an input from pressure sensor 206 upstream of the expansion device 20, an input from pressure sensor 208 downstream of the expansion device, and various other inputs via the vehicle CAN bus. It is also noted that the above described components of controller 500 may simply be implemented as part of the primary vehicle operating system controller and is not necessarily a separate controller.

In operation, the expander bypass valve 202 can be controlled to maintain a pressure differential set point across the expansion device 20, as measured by the difference between the pressure signals received from sensors 206 and 208. The pressure differential across the expansion device 20 directly corresponds to the torque produced by the expansion device 20. Additionally, the operation of the expander bypass valve 202 allows for the backpressure on the power plant exhaust to be controlled such that excessive backpressure is not caused by the expansion device 20 which could result in significant efficiency reductions for the power plant 16. Similarly, the compressor bypass valve 204 can be operated to allow for excess compressed intake air to be diverted back to the intake of the compression device 50 in order to avoid over pressurization of the intake air manifold 13. When the compressor bypass valve 204 is fully open, the ability of the compression device 50 to develop a differential pressure across the compression device 50 is greatly diminished, which also has the effect of lowering the brake horsepower of the compression device 50.

As previously stated, the clutch 93 can be either engaged or disengaged. When the clutch 93 is disengaged, the compression device 50 cannot be driven by the power plant 16. Therefore, the compression device 50 is driven solely by the expansion device 20 when the clutch 93 is disengaged. This mode of operation may be suitable where the power plant is running at a constant load (e.g. vehicle is operating at cruising speed on a highway) and the available waste heat from the power plant 16 is sufficient to drive the compression device 50 solely through the expansion device 20.

When the clutch 93 is engaged, the compression device 50 can be driven by the power plant 16. When the compression device 50 is being driven by the power plant 16, the bypass valve 202 for the expansion device 20 can be opened to reduce the parasitic losses caused by the expansion device 20. Alternatively, and as mentioned previously, a clutch can be provided between the expansion device 20 and the compression device 50 to decouple the devices 20, 50. It is also possible for the expansion device 20 and the power plant 16 to both provide power simultaneously to the compression device 50. Also, when the expansion device 20 is able to generate more power than is required by the compression device or when compression is not needed by the compression device 50, the clutch 93 can remain engaged and the excess power developed by the expansion device 20 can be transmitted through the compression device 50 and back to the power plant 16 via the drive system 90 (e.g. pulleys 91, 16 b and the connected belt 16 c). The bypass valve 204 can be operated to smooth the transition between driving the compression device 50 via the drive system 90 and driving the compression device 50 via the expansion device 20. The above described control and configuration increases the power band range through which the compression device 50 can be operated to boost engine power, thereby increasing engine performance and efficiency.

The detailed description and the drawings or figures are supportive and descriptive of the invention, but the scope of the invention is defined solely by the claims. While some of the best modes and other embodiments for carrying out the claimed invention have been described in detail, various alternative designs and embodiments exist for practicing the invention defined in the appended claims. 

1. An integrated compressor and expander system comprising: a fluid compressor having first and second non-contacting helical meshed rotors, wherein the first rotor is provided with a number of lobes equal to a number of lobes provided on the second rotor; and a volumetric energy recovery device having third and fourth non-contacting helical meshed rotors, wherein the third rotor is provided with a number of lobes equal to a number of lobes provided on the fourth rotor; wherein the first and second rotors of the volumetric fluid compressor are operably connected to the third and fourth rotors of the volumetric energy recovery device such that rotation of the third and fourth rotors causes rotation of the first and second rotors.
 2. The integrated compressor and expander system of claim 1, wherein the first rotor and the third rotor are mounted to a common shaft.
 3. The integrated compressor and expander system of claim 1, further comprising: a first shaft to which the first rotor is mounted; a third shaft to which the third rotor is mounted; and a power transmission link coupling the first shaft to the third shaft.
 4. The integrated compressor and expander system of claim 3, wherein: the power transmission link includes a first transmission gear mounted to the first shaft and a second transmission gear mounted the third shaft.
 5. The integrated compressor and expander system of claim 4, wherein: the first transmission gear is meshed with the second transmission gear.
 6. The integrated compressor and expander system of claim 3, wherein: the power transmission link includes a planetary gear set including a ring gear, a sun gear mounted to the first shaft, and a plurality of planet gears coupled to a common carrier mounted to the third shaft.
 7. The system of claim 6, further comprising a generator in operative connection with the ring gear of the planetary gear set, the generator being configured to vary a rotating speed of the energy recovery device relative to a rotating speed of the volumetric fluid compressor.
 8. The system of claim 6, wherein the generator operates as a brake to vary the rotating speed of the energy recovery device, and wherein the volumetric energy recovery device freewheels when the generator provides zero braking force, thereby reducing drag from the volumetric energy recovery device on the volumetric fluid compressor.
 9. The system of claim 1, further comprising one of a pulley or a gear drive configured to receive torque from a power source, independent of the volumetric energy recovery device, to rotate the volumetric fluid compressor.
 10. The system of claim 9, further comprising an electric drive unit configured to rotate the compressor.
 11. A power-generation system comprising: a power plant employing a power-generation cycle, wherein the power plant uses oxygen to generate power and generates an exhaust gas as a byproduct of the power-generation cycle; a volumetric fluid compressor having first and second non-contacting meshed rotors and configured to generate a stream of relatively high-pressure fluid including oxygen to the power plant, wherein the first rotor is provided with a number of lobes equal to a number of lobes provided on the second rotor; a volumetric energy recovery device having third and fourth non-contacting meshed rotors and configured to be rotated by the exhaust gas to drive the compressor, wherein the third rotor is provided with a number of lobes equal to a number of lobes provided on the fourth rotor; and a power transmission link located between the compressor and the energy recovery device, wherein the link is configured to transfer torque generated by the energy recovery device to the compressor.
 12. The system of claim 11, wherein the power transmission link is one of a gear set and a common shaft extending between the volumetric fluid compressor and the volumetric energy recovery device.
 13. The system of claim 12, wherein the power plant is a fuel cell.
 14. The system of claim 12, wherein the power transmission link is a gear set including a planetary gear structure.
 15. The system of claim 14, wherein the gear set includes: first and second timing gears fixed relative to the first and second meshed rotors, respectively, configured to prevent contact between the first and second rotors; and third and fourth timing gears fixed relative to the third and fourth meshed rotors, respectively, configured to prevent contact between the third and fourth rotors; wherein the first and second timing gears are operatively connected to the third and fourth timing gears via the planetary gear structure.
 16. The system of claim 15, further comprising a generator in operative connection with the planetary gear structure and configured to vary the rotating speed of the energy recovery device to substantially match the rotating speeds of the power plant and the energy recovery device.
 17. The system of claim 16, wherein the generator operates as a brake to vary the rotating speed of the energy recovery device, and wherein the energy recovery device freewheels when the generator provides zero braking force, thereby reducing drag from the energy recovery device on the compressor.
 18. The system of claim 17, wherein the power plant is an internal combustion (IC) engine.
 19. The system of claim 18, further comprising one of a pulley or a gear drive configured to receive torque from the IC engine and rotate the compressor.
 20. The system of claim 11, further comprising an electric drive unit configured to rotate the compressor.
 21. A power conversion unit comprising: a power plant that receives intake air and produces exhaust; a fluid compressor configured to provide pressurized intake air to the power plant; an energy recovery device coupled to the fluid compression device and being configured to convert energy from the power plant exhaust to rotational energy that drives the fluid compression device; a drive system coupling the fluid compression device to a power output location of the power plant, the drive system including a clutch to selectively engage the fluid compression device with the power plant power output location; and a compressor bypass valve configured to recirculate the pressurized intake air from an outlet of the fluid compressor to an inlet of the fluid compressor.
 22. The power conversion unit of claim 21, wherein the power conversion unit has at least a first operational mode and a second operational mode: the first operational mode including the clutch of the drive system being disengaged to decouple the fluid compressor from the power plant power output location; and the second operational mode including the clutch of the drive system being engaged to couple the fluid compressor with the power plant power output location.
 23. The power conversion unit of claim 22, further including: an exhaust bypass valve configured to allow at least a portion of the power plant exhaust to bypass the energy recovery device, the exhaust bypass valve being configured to maintain a differential exhaust pressure set point across the energy recovery device;
 24. The power conversion unit of claim 23, wherein: the first operational mode further includes the exhaust bypass valve being in an open position.
 25. The power conversion unit of claim 22, wherein: the power conversion unit is configured to transfer power from the energy recovery device to the power plant power output location in the first operational mode when the compressor bypass valve is fully open.
 26. The power conversion unit of claim 22, wherein: the compressor bypass valve is configured to open when the power conversion unit transitions from the second operational mode to the first operational mode. 